Potentiometer or the like



2 Sheets-Sheet l Filed May 3, 1954 iso FIG. 3.

INVENToR ALBERT ROBERTS ATTORNEY March l2, 1957 A. ROBERTS POTENTIOMETER OR THE LIKE Filed May 3. 1954 2 Sheets-snee?. 2

FIG. 4.

fnul uuuuuu INVENTOR ALBERT ROBERTS ATTORNEY United States Patent O POTENTIOMETER R THE LIKE Albert Roberts, New York, N. Y.

Application May 3, 1954, Serial No. 427,010

12 Claims. (Cl. y201-48) This invention relates to the art of variable electrical elements and particularly concerns a novel potentiometer, rheostat, variable impedance or the like.

1t is one object of the invention to provide a rheostat or potentiometer providing a finer control and resolution of resistance for a given size than is generally obtainable.

It is a further object to provide a continuously variable electrical element in which an endless helical conductive winding on a toroidal core is rotated on an axis of the toroid while a metal wiper is enabled to move in the same direction, without return or reverse movement, along the winding. Such an element may be a variable resistance, reactance, inductance, impedance, etc.

lt is a further object to provide a potentiometer or the like having a relatively long winding so as to minimize the eiect oi lost motion in the wiper contact of the potentiometer.

lt is a further object to provide a potentiometer or the like which is basically simple in construction, so that it may be manufactured relatively inexpensively.

Other and further objects and advantages of the invention will become apparent from the following description.

Basically the invention includes a toroidal core on which is wound a helical resistance winding. The core is supported on a cylindrical case which carries a circumferentially disposed gear. A control shaft is geared to the circumferential gear and to a geared split ring which carries a wiper contact along the winding in a helical path. As the control shaft is rotated, the winding rotates on the central axis of the toroid and the split ring simultaneously rotates carrying the wiper along the winding.

1n prior known potentiometer structures including a rotatable helical resistance winding and movable conta-ct Wiper, the resistance winding has been directly driven by a control means while the wiper frictionally followed the resistance winding. Some lost motion between winding and wiper has been inevitable. The present invention insures positive, direct and minute control of relative position of resistance winding and contact wiper because both winding and wiper are gear driven by the same control shaft. The invention will be better understood when considered with reference to the drawing wherein:

Fig. 1 is a plan View of a device embodying the invention with a portion broken away to show internal construction.

Fig. 2 is a perspective view showing details of a gear housing embodied in the structure of Fig. l.

Fig. 3 is a sectional view taken on lines 3-3 of Fig. 1.

Fig. 4 is a plan view on an enlarged scale showing details of the structure of Fig. l.

Fig. 5 shows details on an enlarged scale of a split ring gear and drive gear shown in Fig. 4.

Fig. 6 shows a modified form of toroidal core.

Fig. 7 shows modied forms of end plates for the gear housing.

In Fig. 1 is shown the cylindrical casing 10 having a circular cover plate 11. The plate 11 is shown partially broken away to reveal the control shaft 12 which carries a control knob or handle 13 at one end, a bevel gear 14 at an intermediate position and a spur type gear 15 lodged in the gear housing 27 at its other end. Gear 15 is best shown in Figs. 3, 4, 5 and will be further discussed later. A toroidal core 17 is supported by a plurality of radial spokes 18. A resistance element is wound on core 17 to form the helical winding 19. Spokes 18 are welded, soldered or otherwise attached to a rotatable cylindrical cup member 20 which carries the bevel gear 21 tted to the outer wall of the cup member.

In Fig. 5 is shown the cylindrical cup member 20 provided with a collar 23 at its lower end in which is locked the shaft 22. Shaft 22 is journaled in the aperture 25 of cylindrical casing 1@ and in a recess 26 of the housing 27.

Housing 27 is a substantially rectangular block structure formed of plastic fiber or other insulation material. It has an upper section 2S and a lower section 29. A plurality of bore holes are provided in the several sections. l'n hole 3@ is lodged the gear 15. Hole 31 is formed by the upper and lower sections of housing 27. Through this hole passes the toroidal core 17, and around the core in hole 31 rotates the split ring gear 32.

ln Fig. 4 is shown clearly the housing 27. The two part structure 28, 29 is necessary in order to mount the toroidal core in hole 31. The wall; of holes 34E, 31 overlap so that the teeth of split ring gear 32 engages thcs: of gear 15. End plates 33 and 34 hold the several housing sections together since they are provided with apertures 35 and 37 which register with apertures 36 in the housing sections to receive suitable bolts or screws A hole 63 is provided in plate 34 through which passes shaft 12. Plates 33, 34 are also provided with holes 31', 31 which register with hole 31 in housing 27. At one side of housing 27 is a recess 3S through which passes the toroidal core 17. Registering recesses 33 and 38 are provided in plates 33, 34 respectively. At the opposite side of the housing a slot 39 is provided between the sections 28, 29 opening into hole 31 through which passes spokes 18 during movement of the toroidal core. Screws 41 are threaded in apertures 42 of housing section 2S and serve to secure the housing to cover plate 11 as shown in Figs. 2 and 3.

ln Figs. 4 and 5 are clearly shown the gears 15 and 32. Gear 32 is in the form of a generally circular split ring with ends 43 spaced apart but overlapping circumferentially. The inner diameter of ring gear 32 is slightly larger than that of the toroidal core 17 with its winding 19. The teeth 44 of gear 32 mesh with teeth 45 of gear 15. The Width or axial extent of gear 15 is at least equal to the greatest width of gear 32 at its ends 43. In order to prevent sidewise movement of gear 32 it is provided with a pair of pins 46 which project radially from gear 32. These pins slide in a circumferential single turn groove 47 disposed transversely of teeth 45 in gear 15. A single turn groove 4S is provided in the wall of hole 31 in housing 27. The pins 46 project into this groove, so that throughout movement of gear 32 at least one pin 46 is always either in groove 47 or 48. Groove 48 is located at the bottom 16 of a wider groove having sides 49 between which ride the gear 32 so that it is continually constrained from sidewise movement during rotation.

The electrical system of the device will now be described. The helical coil 19 may be a continuous winding or may have separate terminations. The electrical conductors 50 are joined to winding 19 and pass through boreholes 54 in core 17 and boreholes 55 in spokes 18. Conductors 50 terminate in circular slip rings 51, 52 mounted rigidly outside cylindrical member 2d. Stationary brushes 53 mounted in case 10 contact the slip rings and are connected to conductors 56 which pass through case 10 for connection to a suitable electrical circuit. Although only two electrical leads are shown connected to winding 19, as many leads as desired may be connected to the winding and brought out to slip rings. The split ring gear 32 has mounted on its inner periphery a spring member 57 shown in Fig. 3 which carries a wiper contact element S8. Contact element S8 slides on the resistance winding 19 as gear 32 rotates. A pair of spring wipers 59 are disposed on opposite sides of gear 32 and are carried by the housing 2'7. The wipers are joined electrically by conductor 6l) which is connected to conductorV 61 and the latter extends through the structure 23, 29 and thence out through casing lll in the form of a lead.

In operation, handle 13 which is secured on shaft l2 by a set screw 65 is rotated causing rotation of gears 14 and l5. Gear lid in engagement with bevel gear 21 causes rotation of the cylindrical cup member Ztl, and the toroidal core i7 rotates on the axis of the cup member in recess 3S and hole 3l of the housing 27. Atthe same time gear 15 causes rotation of the split ring gear 32 so that wiper contact S8 follows the winding i9 along its length. As wiper Contact d8 traverses the winding 19, electrical current is conducted via wiper Contact S, gear 32 and either one of wipers 5S, SBthrough conductors 60 and 6l. rl`he electrical energy may be supplied to the winding via leads 56 which are connected in circuit with leads Si) and winding 19. As an alternative electrical arrangement one ot leads 5'6 and the lead 61 may be connected to an outside source of electrical current. The electrical path will then be from lead 6l through gear 32, wiper Contact 53, winding l@ and lead S@ to the lead 56 selected as the other circuit connection. Many other electrical arrangements are possible and will readily occur to those skilled in the art.

ln Fig. 6 is shown a preferred form of toroidal core. rl`he'core l? is provided with a removable segment 17 so that the slip ring gear 32 can be mounted over the core and the segment 217' is then replaced. instead of providing a removable segment the core can be made in one piece as a complete toroid, and the ring gear 32 can be made of two parts secured together after being mounted on the core. The winding in 1Eig. 6 has the alternative form of a mandrel in the form of a helix 66 of non-conductive material on which is wound the resistance element l.

in Fig. 7 the alternative form of side plates 33' and 35i' are shown which replace the plates 33, 3.4i respectively. These T-shaped plates 33', 34 serve the same functions as plates 33, to ioin the several sections ot housing 2,7 but they permit easier assembly of the several parts since apertures 3l and 3l are omitted. Apertures 36 should be located in housing sections 28, 29 to register with the apertures 35, 37 in plates 33', 34.

The cylindrical cup member Ztl may be made of conduetive or non-conductive material. lf it is made of conductive material such as copper, aluminum or the like, the bottom or the cup should be made of insulation material or the insulation spacers 67 should be provided between slip rings 531, 52, 62 and the bottom of cup member if cup member Ztl is made of insulation material, the insulation spacers may be omitted. All leads such es 5l?, S6, 6u, 6l, should be insulated conductors. Resistance elements E9 and i9 are bare wire, Core 17 as well as housing 27 including Sections 2S, 29 and plates 33, 34 or 33, 3ft are made of insulation material such as plastic, ber and the like.

In order to insure that sliding contact 58 follows the path of the helical resistance element 19 as closely as possible, the pitch of the helix should be small relative to its length. it is also possible to modify the circular cross section of the toroid in a manner which compensates for any deviation between the path of the sliding contact and that of the helix.

Although the invention has been described with reference to a potentiometer or rheostat which is a variable resistance, it will be readily apparent to those skilled in 4-y the art that the device is adapted to serve as a variable inductance, impedance or other variable electrical element.

Although only a limited number of embodiments of the invention have been disclosed it is not intended that the invention be limited thereto since they are only illustrative of the invention. The scope of the invention is defined in the appended claims.

I claim:

l. A potentiometer or the like comprising a shaft, a pair of gears carried by the shaft, a cylindrical member carrying a circular gear engaged with one of said gears, a helical conductive coil carried by the cylindrical member, a split ring gear encircling the Vcoil and engaged with another of said pair of gears, and an electrical Contact carried by the ring gear to contact the coil along its length during rotation of said shaft.

2. A potentiometer or the like comprising a member carrying a conductive coil and a circular gear disposed circumferentially around the coil, a split ring gear encircling the coil and in electrical contact therewith, and means engaging the circular and ring gears to rotate the coil and ring gear simultaneously.

3. A potentiometer or the like comprising a shaft, a bevel gear and spur gear carried by the shaft, a circular gear in engagement with the bevel gear, a ring gear in engagement with the spur gear, said ring gear encircling a toroidal helical conductive coil and electrically contacting the coil,

4. A potentiometer or the like comprising a rotatable shaft, a pair of gears carried by the shaft, a circular gear in engagement with the bevel gear and operatively connected to a toroidal helical conductive coil, a ring gear in engagement with the other of said pair of gears, and encircling said coil, said ring gear electrically contacting said coil and a non-conductive housing provided with means for confining movement of said ring gear in a circular path during rotation of said shaft.

5. A device according to claim 3, wherein said coil is disposed transversely of said housing and passes therethrough during rotation of said shaft.

6. A device according to claim 5, wherein said other gear rotates within said housing.

7. A device according to claim 3, further comprising a cylindrical member carrying said circular gear and supporting slip rings electrically connected to said coil and ring gear, said member being rotatably mounted in a case, and stationary electrical contacts carried by the case and contacting said slip rings.

8. A device according to claim 3, wherein said conductive coil is an electrical resistance element.

9. A variable electrical element, comprising an annular core, a helical conductive member wound on the core, the axis of said helical conductive member comprising a circular line which is equidistant at all points from the central axis of the annular core, a ring encircling said core and conductive member and carrying an electrical Contact, the axis of the ring being tangential to said circular line, and means for rotating said ring about its said axis to move the contact along the conductive member in a substantially helical path.

l0. A variable electrical element, comprising a toroidal helical conductive member whose central axis comprises a circular line, a ring encircling said helical conductive member and carrying an electrical contact engageable` with said helical conductive member, the central axis of said ring being tangential to said circular line, and means for rotating the ring about its said axis to move said electrical Contact along said helical conductive member in a substantially helical path.

ll. A potentiometer or the like, comprising a toroidal helical conductive member whose axis comprises a circular line, a ring encircling and contacting said helical conductive member, the axis of the ring being tangentialv to said circular line, and means for rotating'thering'abo'ut its Said axis to effect Contact with the helical conductive means for rctating the ring in a helical toi'oidal path to member along its entire length. move it along and in Contact with said toroidal conductive 12. A potentiometer or the like, comprising a toroidal helix.

conductive helix, a ring encircling and contacting the helix, References Cited in the file of this patent the width of the ring being at least equal to the width of a single convolution of said helix and the axis of the ring coinciding with the convolution which it encircles, and

UNITED STATES PATENTS 2,595,189 Dewan Apr. 29, 1952 

